The overall aim of this sub-project focuses on gene isolation and molecular analysis of the proximal half of the long arm of human chromosome 21 including 21q11-21, a region under-exploited but associated with mental retardation of individuals with Down Syndrome. The specific objectives are: (1) Isolation, characterization and sequencing of unique sequence microclones from microdissection libraries constructed specifically for the 21q11-21 region; (2) Homology analysis between the unique copy microclones and know genes or cDNAs; (3) refined regional mapping of microclones within 21q11-21; (4) comparative mapping between 21q11-21 and the mouse genome; (5)methylation analysis of 21q11-21; (6) chromatin condensation analysis of 21q11-21 during interphase; (7) isolation and characterization of CDNAS from 21q11-21; (8) gene expression analysis using demetylation strategies; (9) study of the genomic structure and organization of 21q11-21 relating to its function and regulation; (1) analysis of genes and cDNAs identified in 21q11-21 for possible involvement in cognitive-neural developmental deficits in mental retardation. Promising progress towards most of these objectives have already been made to demonstrate that the 21q11-21 region indeed have genes which may be important to Down syndrome. These studies also showed that 21q11-21 has unique structures which may be crucial to the regulation of the genes residing in this region. Thus, gene isolation and better understanding of the regulation and expression of 21q11-21 should be important to the unraveling of the etiology of mental retardation in Down syndrome and for possible early intervention of this devastating pathology.